Shindengen Electric MFG.CO.,LTD

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3.1 Startup circuit

In a conventional startup circuit employing a startup resistor,

an electric current continues to flow after the power supply

starts, wasting power and reducing efficiency, especially

during standby.

See [Conventional startup circuit] in Fig. 3.1 Comparison of

startup circuits.

In the MR4000 Series startup circuit, the startup current is

supplied from the input voltage and shut off when the power

supply starts up.

internally in the IC and also used as the charging current for

GND. This design allows stable startup with minimal

dependence on the input voltage.

current is halted. As soon as it stops, oscillation begins.

The current to be consumed in the IC is then supplied from

the control coil.

See [MR4000 startup circuit] in Fig. 3.1 Comparison of

startup circuits.

In the case of an instantaneous power failure or a load short,

Incorporating the functions above improves efficiency, particularly during standby, and eliminates the need for a startup

resistor, thereby reducing the overall number of components.

[Conventional startup circuit]

IC

Startup current

The startup current flows even

during steady-state operation,

resulting in losses.

Vin pin

[MR4000 startup circuit]

Control coil

7

4

The startup current switches off

after startup, eliminating the

need for a startup resistor.

Fig. 3.1 Comparison of startup circuits

[Vin]

=

Load short

Instantaneous

power failure

Fig. 3.2 Startup circuit operation sequence

3. Operating principles

MR4000 Series

Application Note